Question

Predict in which of the following, entropy decreases:

• A. $2NaHCO_3(s) Na_2CO_3(s) + CO_2(g) + H_2O(g)$
• B. Temperature of a crystalline solid is raised from 0 K to 115 K.
• C. A liquid crystallizes into a solid.
• D. $H_2(g)→2H(g)$
• E. $2SO_3(g)→2SO_2(g) + O_2(g)$

Answer 1

The Correct Option is C

Entropy is a measure of disorder or randomness in a system. A process in which disorder decreases will result in a decrease in entropy.

Let’s analyze each case: 

1. A liquid crystallizes into a solid: Disorder decreases because a liquid is more disordered than a solid. Entropy decreases.
2. Temperature of a crystalline solid is raised from 0 K to 115 K: Entropy increases as the particles gain energy and vibrate more. Entropy increases.
3. \( 2NaHCO_3(s) \rightarrow Na_2CO_3(s) + CO_2(g) + H_2O(g) \): Gases are formed, so disorder increases. Entropy increases.
4. \( H_2(g) \rightarrow 2H(g) \): Bonds are broken and atomic particles are formed, increasing randomness. Entropy increases.
5. \( 2SO_3(g) \rightarrow 2SO_2(g) + O_2(g) \): Number of gas molecules increases, leading to higher disorder. Entropy increases.

Correct Prediction:

Entropy decreases in: A liquid crystallizes into a solid